scholarly journals Rheology of a Dilute Suspension of Aggregates in Shear-Thinning Fluids

Micromachines ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 443 ◽  
Author(s):  
Marco Trofa ◽  
Gaetano D’Avino
Keyword(s):  
Fractal Dimension ◽  
Intrinsic Viscosity ◽  
Shear Thinning ◽  
Flow Index ◽  
Kinematic Equation ◽  
Shear Thinning Fluids ◽  
Fractal Parameters ◽  
Angular Velocities ◽  
Dilute Suspension ◽  
Particle Orientations

The prediction of the viscosity of suspensions is of fundamental importance in several fields. Most of the available studies have been focused on particles with simple shapes, for example, spheres or spheroids. In this work, we study the viscosity of a dilute suspension of fractal-shape aggregates suspended in a shear-thinning fluid by direct numerical simulations. The suspending fluid is modeled by the power-law constitutive equation. For each morphology, a map of particle angular velocities is obtained by solving the governing equations for several particle orientations. The map is used to integrate the kinematic equation for the orientation vectors and reconstruct the aggregate orientational dynamics. The intrinsic viscosity is computed by a homogenization procedure along the particle orbits. In agreement with previous results on Newtonian suspensions, the intrinsic viscosity, averaged over different initial orientations and aggregate morphologies characterized by the same fractal parameters, decreases by increasing the fractal dimension, that is, from rod-like to spherical-like aggregates. Shear-thinning further reduces the intrinsic viscosity showing a linear dependence with the flow index in the investigated range. The intrinsic viscosity can be properly scaled with respect to the number of primary particles and the flow index to obtain a single curve as a function of the fractal dimension.

Influence of Fluid Parameters on Vortex Shedding and Other Characteristics of a Herschel-Bulkley Fluid Flow Over a Circular Cylinder

2013 ◽  
Author(s):  
Raed I. Bourisli
Keyword(s):  
Circular Cylinder ◽  
Reynolds Numbers ◽  
Shear Thinning ◽  
High Yield ◽  
Flow Index ◽  
Qualitative Behavior ◽  
Shear Thinning Fluids ◽  
Flow Parameters ◽  
Fluid Behavior ◽  
Fluid Parameters

Unsteady flow of a Herschel-Bulkley fluid over a stationary, smooth circular cylinder is studied numerically. The effects of fluid parameters such as the Oldroyd number, Od, and the flow index, n, on the flow morphology and various dynamic coefficients are examined. It is found that for shear-thinning fluids (high modified Reynolds numbers) and high Oldroyd numbers (high yield-stress), the flow parameters such as drag and skin-friction coefficients exhibited rather complicated behavior, often with bi- and tri-frequencies. Strouhal number dependence on these parameters was quantified and found to be consistent with recent reported results in the lower Re regime; its qualitative behavior mirrored for the most part what Newtonian fluids did in the range of Re investigated. Physical explanations are given as to why the departure from Newtonian, or simple non-Newtonian fluid, behavior is observed — mainly the combined effect of shear-thinning and the presence of regions of unyielded fluid.

scholarly journals Effect of Surfactants on Gas Holdup in Shear-Thinning Fluids

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Shaobai Li ◽  
Siyuan Huang ◽  
Jungeng Fan
Keyword(s):  
Experimental Data ◽  
Liquid Phase ◽  
Sodium Dodecyl ◽  
Shear Thinning ◽  
Gas Holdup ◽  
Bubble Columns ◽  
Gas Velocity ◽  
Shear Thinning Fluids ◽  
Liquid Surface Tension ◽  
Superficial Gas Velocity

In this study, the gas holdup of bubble swarms in shear-thinning fluids was experimentally studied at superficial gas velocities ranging from 0.001 to 0.02 m·s−1. Carboxylmethyl cellulose (CMC) solutions of 0.2 wt%, 0.6 wt%, and 1.0 wt% with sodium dodecyl sulfate (SDS) as the surfactant were used as the power-law (liquid phase), and nitrogen was used as the gas phase. Effects of SDS concentration, rheological behavior, and physical properties of the liquid phase and superficial gas velocity on gas holdup were investigated. Results indicated that gas holdup increases with increasing superficial gas velocity and decreasing CMC concentration. Moreover, the addition of SDS in CMC solutions increased gas holdup, and the degree increased with the surfactant concentration. An empirical correlation was proposed for evaluating gas holdup as a function of liquid surface tension, density, effective viscosity, rheological property, superficial gas velocity, and geometric characteristics of bubble columns using the experimental data obtained for the different superficial gas velocities and CMC solution concentrations with different surfactant solutions. These proposed correlations reasonably fitted the experimental data obtained for gas holdup in this system.

Stability of Shear-Thickening Liquids Between Rotating Cylinders

2010 ◽  
Author(s):  
Nariman Ashrafi ◽  
Habib Karimi Haghighi
Keyword(s):  
Couette Flow ◽  
Dynamical Behavior ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Taylor Vortex ◽  
Shear Dependent Viscosity ◽  
Shear Thinning Fluids ◽  
Shear Thickening Fluids ◽  
The Stability ◽  
Dependent Viscosity

The effects of nonlinearities on the stability are explored for shear thickening fluids in the narrow-gap limit of the Taylor-Couette flow. It is assumed that shear-thickening fluids behave exactly as opposite of shear thinning ones. A dynamical system is obtained from the conservation of mass and momentum equations which include nonlinear terms in velocity components due to the shear-dependent viscosity. It is found that the critical Taylor number, corresponding to the loss of stability of Couette flow becomes higher as the shear-thickening effects increases. Similar to the shear thinning case, the Taylor vortex structure emerges in the shear thickening flow, however they quickly disappear thus bringing the flow back to the purely azimuthal flow. Naturally, one expects shear thickening fluids to result in inverse dynamical behavior of shear thinning fluids. This study proves that this is not the case for every point on the bifurcation diagram.

An analytical theory for the forced convection condensation of shear-thinning fluids onto isothermal horizontal surfaces

2022 ◽  
Vol 421 ◽  
pp. 126909
Author(s):  
Uttam Kumar Kar ◽  
Sayantan Sengupta ◽  
Shantanu Pramanik ◽  
Soumik Chakraborty
Keyword(s):  
Forced Convection ◽  
Shear Thinning ◽  
Analytical Theory ◽  
Shear Thinning Fluids
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